Work-related musculoskeletal disorders due to repeated hand tasks involve primarily the tendons of the fingers and the wrist, yet there are no measures of the load experienced by these tendons that are relevant to the occupational setting. Current methods of estimating forces in these tissues use biomechanical models or surface electromyograms, neither of which has been validated. The principal investigator proposes to directly measure index finger flexor tendon force at the wrist in 40 subjects undergoing hand surgery while the subjects perform specific hand tasks. Fingertip force and finger posture will also be recorded. First, a pinch grip task will be repeated at different force levels, finger postures, and loading rates. Second, switches of different design will be repeatedly activated by the finger. Task conditions are selected that can be generalized to the workplace. The effect of these task conditions on tendon force and the ratios of fingertip to tendon force will be evaluated. Combined with the finger posture data, the information will also be used to evaluate existing biomechanical models. If the accuracy of the models is poor, then modified models or new models will be proposed. The ultimate goal is to determine the dose-response relationships of fingertip load to tendon load in order to provide guidelines for hand tool design and tool use to minimize tendon loading, and thereby reduce the risk of developing tendon related disorders. The proposed study is a collaborative effort between the University of California Ergonomics Program (UCSF), Hand and Microsurgery (UCSP), Mechanical Engineering (UC Berkeley), and the Smith-Kettlewell Eye Research Institute.